1. Field of the Invention
The present invention relates to a spin valve sensor with a nickel oxide (NiO) pinning layer on a chromium based seed layer and more particularly to a chromium seed layer that improves an exchange coupling between the pinning layer and a pinned layer of the sensor.
2. Description of the Related Art
A spin valve sensor is employed by a read head for sensing magnetic fields on a moving magnetic medium, such as a rotating magnetic disk. The sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer is exchange coupled to the pinned layer for pinning the magnetic moment of the pinned layer 90.degree. to an air bearing surface (ABS) which is an exposed surface of the sensor that faces the magnetic disk. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetic moment of the free layer is free to rotate upwardly or downwardly with respect to the ABS from a quiescent or bias point position in response to positive and negative magnetic field signals from a rotating magnetic disk. The quiescent position, which is typically parallel to the ABS, is the position of the magnetic moment of the free layer with the sense current conducted through the sensor in the absence of signal fields.
The thickness of the spacer layer is chosen so that shunting of the sense current and a magnetic coupling between the free and pinned layers are minimized. This thickness is typically less than the mean free path of electrons conducted through the sensor. With this arrangement, a portion of the conduction electrons are scattered at the interfaces of the spacer layer with respect to the pinned and free layers. Changes in scattering changes the resistance of the spin valve sensor as a function of cos .theta., where .theta. is the angle between the magnetic moments of the pinned and free layers. When the magnetic moments of the pinned and free layers are parallel with respect to one another scattering is minimal and when their magnetic moments are antiparallel scattering is maximized. The sensitivity of the sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in resistance of the sensor from a minimum resistance, where the magnetic moments of the free and pinned layer are parallel, to a maximum resistance, where the magnetic moments are antiparallel, and R is the resistance of the sensor before the change.
Over the years a significant amount of research has been conducted to improve the magnetoresistive coefficient dr/R (also referred to as GMR) of spin valve sensors. These efforts have increased the storage capacity of computers from kilobytes to megabytes to gigabytes. Some of these efforts have been directed to the type of material and thicknesses of the various layers of the spin valve sensor which is an effort of the present invention.